The present invention relates to a bearing plate for a band of photoconductive recording medium which travels around in an endless loop and is provided with perforations close to and parallel to one of the two longitudinal edges, and in which a metal brush presses against the recording medium in the zone of the perforated longitudinal edge.
In electrophotographic copying devices, bands of photoconductive recording media are used, such as, for example, organic photoconductor bands in the form of endless belts. The timing sequence and the mutual synchronization of the individual process steps are effected by means of electric contacts. For this purpose, the use of an organic photoconductor which has a number of holes along its front edge has been disclosed in the papers read at the annual meeting of IEEE Industry Applications Society in October 1977. These are standard perforations, such as are conventionally used in 35 mm films. These perforations represent a means for generating time signals which are related to the motion of the band. This known organic photoconductor consists of a photoconductive layer, an electrically conductive layer lying below it, and a support layer. In addition to the perforations of usual length, there are also six perforations of double the length. These six perforations of double length emit signals to the microprocessor system of the electrophotographic copying machine in which the photoconductor band is used, these signals triggering inter alia the flash exposures of six imaging elements along the length of the photoconductor tape. Between every pair of perforations of double length, there are fifty standard perforations, and the signals triggered by these perforations are utilized for controlling the timing sequence of the remaining process steps.
The electrical connection of the support layer of the photoconductor band is made by a wire brush which is in contact with a strip applied along the edge of the photoconductor band.
The time signals are generated by means of a twin sensor. The latter is actuated by a hammer which presses against the photoconductor band along the perforations under a slight pressure. When a perforation passes through under the hammer, the latter strikes the bearing plate on which piezo-electric strips are fitted. The strips of a piezo-electric ceramic material are polarized in mutually opposite directions in order to generate an electric signal of corresponding magnitude on each actuation of the hammer, and they are components of the hammer arrangement. The hammer exerts very small forces on the photoconductor band so that there is no destruction. The generation of signals is stable over a very large number of actuations of the hammer and is not prone to soiling and environmental influences. It can be seen, however, that the use of piezo-electric ceramic strips necessitates a downstream amplifier or a high-resistance and hence fault-prone line, and as a result of which, the manufacturing costs also rise.
A process for the sectional operation of a band of photoconductive recording medium in an electrophotographic copying machine is known from German Auslegeschrift No. 2,220,909. There the passage or the motion of the recording medium is controlled by means of markings formed in or on the recording medium, which markings are identified by a reader device and are converted into data which control the forward motion. In this case, the markings are formed only during the passage of the tape-like recording medium in the copying machine itself, for each desired size of format and exactly at the correct point.
A tape-like recording medium which, for controlling the forward motion, has markings which can be electrically conductive markings, perforations or the like, and which are made on the recording medium before it is installed, is known from German Auslegeschrift No. 1,263,509.
If a band of photoconductive recording medium with holes or perforations is used, in connection with which contact brushes of metal slide at the level of the holes on the surface of the photoconductor, and the photoconductor moves along the surface of a grounded metal plate, a contact is made as the result of the metal contact brush touching the metal plate at the points of the perforations. The contact arises with low resistance and can be directly further used electrically, without a high-resistance line or an amplification being necessary. In this case, however, faults can occur on prolonged copying operation due to soiling with toner, caused by the fact that toner gets into the holes and is transported with the photoconductor band and deposits on the metal plate and on the contact brushes. The result of this is a break of the electric contact between the contact brushes and the metal plate.